Cam phasers vary the valve timing of internal combustion engines and may help reduce nitrogen oxides (NOX) and other emissions such as unburned hydrocarbons. Cam phasers also help improve fuel economy and/or increase engine torque at various speeds. Multiple cam phasers may be used to actuate intake and exhaust valves on an internal combustion engine.
A phaser typically comprises a rotor element that is attached to the end of a camshaft and is variably displaceable rotationally within a stator element driven by the engine crankshaft. Cam phasers are typically actuated by pressurized oil from the engine's main oil supply. The oil is selectively directed by electronically controlled valving to chambers within the phaser. The direction of the oil alters the phase relationship between the rotor and stator, and, hence, between the camshaft and crankshaft.
A current method of controlling cam phasers employs a traditional proportional and integral (PI) gains calculation for each phaser. Although widely used, this calculation is still susceptible to overshoot and undershoot. Furthermore, this method of calculation requires a substantial amount of controller memory and processing capacity. Moreover, the PI gain calculation increases the complexity of calibrations used to control the cam phaser.